Computers often have peripheral devices connected to them. Some peripheral devices are on cards that are plugged into slots, and other peripheral devices are located on the main circuit board within the computer. This main circuit board, which is typically called a “motherboard,” usually has a processor attached.
Some peripheral devices can have one or more predefined capabilities that can be queried by the processor. For example, peripheral devices compliant with revision 2.2 of the peripheral component interconnect (PCI) local bus specification (published Dec. 18, 1998 by PCI Special Interest Group, Portland, Oreg.) may indicate one or more special predefined capabilities using a list of capabilities implemented in hardware and accessible by certain types of software. Examples of defined capabilities include power management, Advanced Graphics Processing (AGP), and PCI-X, which is a variation of PCI. In operation, software such as operating systems and device drivers may query a PCI peripheral device to determine if a particular capability is supported.
Capabilities lists are typically implemented as a set of defined groups of read-only registers. Each group of read-only registers for a given capability contains an address pointer to the next group of capabilities registers, forming what is commonly referred to as a linked list. The linked list is typically physically implemented as a read-only memory (ROM). These linked lists are generated during manufacture of the peripheral device, or during a one-time program operation, typically performed shortly after manufacture. As a result, the linked lists, and associated list of peripheral device capabilities cannot be modified after the peripheral device is resident in a computer system.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternate hardware linked list implementations.